This business over the timing belt. My instinctive reaction to reading this post was NO the timing belt must be changed at 6 years or 60K miles, whichever is sooner. On checking my service history sheets I find that up until 2005 Lexus were saying 6 years or 100K miles, whichever is the sooner. In 2005 they say 10 years or 100K miles, whichever is the sooner. Unfortunately I don't have the schedules for 2006 onwards. So if it hasn't been changed, then you don't need a belt change.
Has anybody else got the 2006 onwards service sheets?
If your car is out of warranty, I would go to a good independent. IS200's are very familiar to the motor trade and you will save a fortune.